Hitherto, synthesis of acetals having the structure shown below has not been sufficiently studied. One general method therefor is described in JP-A-5-313322 ("JP-A" means an unexamined published Japanese patent application). ##STR2##
Specifically, as shown in scheme (I) below, it was a method wherein (A) was subjected to methylolation with paraformaldehyde, to synthesize (B), and the resultant (B) was reacted with mercapto azole in the presence of zinc iodide, to obtain (C) as an objective product. ##STR3##
However, the above-described method had such problems that
(i) Two steps are necessary to obtain the object, PA1 (ii) The yield is low in each of the steps, PA1 (iii) It is extremely difficult to isolate (B) using a means other than column purification, because (B) of an intermediate is synthesized with a low yield and poor crystallinity, PA1 (iv) Paraformaldehyde is adhered onto a cooling tube during the synthesis of (B), and PA1 (v) Unless the purity of (B) is increased, the synthesis reaction of (C) does not go well. PA1 (1) The yield is not satisfactory, and PA1 (2) It causes a heavy load on environment, at the dealing and disposal of metal salt (heavy metal) used as a catalyst. PA1 (1) A method of producing acetals, comprising reacting a compound represented by formula (I), at least one compound selected from a group consisting of a compound represented by formula (II), paraformaldehyde, and trioxane; and a compound represented by formula (III), to synthesize an acetal represented by formula (IV), wherein the reaction is carried out in the presence of an oxidizing agent and an acid; ##STR4## PA1 (2) The method of producing acetals as stated in the above (1), wherein R.sup.1 is represented by formula (VI): ##STR8## PA1 (3) The method of producing acetals as stated in the above (1), wherein the oxidizing agent is a peroxide; and PA1 (4) The method of producing acetals as stated in the above (1), wherein the oxidizing agent is a hydrogen peroxide, or an addition product thereof.
Compared to such a conventional method, JP-A-5-331145 describes a method in which a reaction is efficiently carried out using a metal salt, whose typical example is copper bromide, as a catalyst. However, this method still has such problems that